A high-precision positioning system plays more and more important role in nowadays high technological fields, such as IC manufacturing process, home entertainment systems, including DVD and VCD players, etc. Currently, there are already developed many precision positioning technologies that adopt, for example, a piezoelectric actuator, which not only enables a definition as high as 10 nanometers within a travel distance of only 10 micrometers, but also has fast response. However, the piezoelectric actuator allows only a limited travel distance, and is therefore not suitable for the applications that require a relatively large travel distance. To meet the requirement for long travel distance, a traditional way is to use a servo motor and a cooperating lead screw, or to use a linear motor. However, since the lead screw is subject to the backlash phenomenon and the friction between bearings, the overall positioning precision is obviously lowered. On the other hand, the linear motor is subject to the ripple effects and the end-effects to thereby cause lowered positioning precision.
To overcome the above system problems, the use of a non-contact force is apparently a somewhat good solution. Among others, the pneumatic levitation system, the electrostatic levitation system, and the magnetic levitation system are the most common examples of utilization of non-contact force. However, the first two systems are not suitable for use in some special environments, such as dust-free room, vacuum environment, etc. Therefore, for the purpose of developing a high precision positioning system usable in a variety of environments, the present invention provides a system employing the magnetic levitation principle to construct its basic configuration. In recent years, more and more researches have been conducted to develop magnetic levitation systems. With the superior characteristics of the non-contact force, some of the technologies that have been considered as being unable to have further breakthrough could have remarkable development now. Some examples of such technologies include the wind tunnel system employed in aerospace and automobile industries, high-precision positioning system, big-scale speedy transiting system, bearings, and shock-absorbing system.
In the past, the inventors of the present invention had already developed a single-layer and single-axis magnetic levitation system as well as a dual-layer and dual-axis six-degree-of-freedom magnetic levitation system. While these two systems are theoretically and experimentally excellent, they still have some inherent defects that could not be easily overcome, such as low structural strength, complicated mechanism design, and relatively high power consumption. A currently available and relatively matured dual-axis magnetic levitation technology is the six-degree-of-freedom magnetic levitation positioning platform developed by Dr. Trumper of Massachusetts Institute of Technology in 1996 (referring to Won-jong Kim, David L. Trumper, “Active Multivariable Optimal Control of a Planar Magnetic Levitator.”, Proc. of the IEEE Int. Conf. on Control Application, October 1997, and Trumper, D. L. and Kim, W.-J., “Magnetic Positioner Having a Single Moving Part”, U.S. Pat. No. 6,003,230, Dec. 21, 1999.) The system of Dr. Trumper uses a linear motor as its basic configuration to simultaneously provide the vertical levitation force and the lateral driving force needed by the magnetic levitation system. However, this system involves in complicated and highly difficult fabricating procedures, and is therefore not easily widely accepted by related industrial fields.
Mr. Won-jong Kim, a student of Dr. Trumper, has also developed at University of Texas a new model of six-degree-of-freedom micro-actuator, which is now still in the research and development stage (referring to Won-jong Kim, “Precision Dynamics, Stochastic Modeling, and Multivariable Control of Planar Magnetic Levitator.” Proc. of the American Control Conf., May 2002, and S. Verma, K. Won-jong, and H. Shakir, “Multi-axis maglev nanopositioner for precision manufacturing and manipulation applications.” Industry Applications, IEEE Transactions on, vol. 41, pp. 1159-1167, 2005). The system developed by Kim uses the magnetic effect between coils and permanent magnets to achieve motions in six degrees of freedom. While it is expected this system would be able to meet the requirement of high precision, the hardware mechanism design for this system is restricted by the inherent limitation in travel distance, and is therefore not suitable for applications involving a large travel distance.
Finally, Professor Menq of Ohio University also has developed a magnetic levitation positioning system (referring to S. Ximin, K. Shih-Kang, Z. Jihua, and M. Chia-Hsiang, “Ultra precision motion control of a multiple degrees of freedom magnetic suspension stage,” Mechatronics, IEEE/ASME Transactions on, vol. 7, pp. 67-78, 2002). The system of Professor Menq utilizes the principle of linear motor to generate the lateral force and the large-scale electromagnetic coil to generate the vertical force. However, a biggest disadvantage of this system is its relatively complicated mechanism design and high manufacturing cost. Moreover, the system of Professor Menq has higher power consumption compared to the other two systems, and is therefore not economical for use.
In summary, the magnetic levitation positioning systems of prior art have one or more of the disadvantages of limited travel distance, complicated structural design, high manufacturing cost, and high power consumption. It is therefore tried by the inventor to develop a six-degree-of-freedom precision positioning system that has simple configuration, low manufacturing cost, low power consumption, and the ability of achieving long travel distance while providing high-precision positioning performance.